Enhanced production of Serratia marcescens chitinase in PEG/dextran aqueous two-phase systems

Abstract

Extractive bioconversion was carried out in 2% (w/w) PEG 20,000 and 5% (w/w) dextran T500 aqueous two-phase systems (ATPS) for the production of extracellular chitinase from Serratia marcescens. Fermentation results were compared in the polymer-free reference system, the ATPS, and a polymer solution of PEG or dextran simulating the top and bottom phases of the ATPS. The cell growth and enzyme production kinetics were similar in all systems. However, enhanced enzyme production was observed in the presence of either polymer. Compared to the maximum enzyme activity in the reference system, the activities were 2.5, 1.9, and 3.1 times as high in the dextran solution, the PEG solution, and the ATPS, respectively. The mechanism responsible for the enhanced production of chitinase in ATPS was investigated. It is not caused by increased activity and stability of the enzyme, less adsorption of enzyme to chitin, or less protease production by the cells. PEG was found to cause cell autolysis, but this may represent only one of the effects of polymers on fermentation. Semicontinuous production of chitinase was carried out with repeated batch fermentation by intermittently removing the bottom phase, replenishing the fresh bottom phase containing chitin, and recycling the cell-containing top phase. This resulted in increasing enzyme activity and productivity in successive batches as a result of the removal of the inhibitory metabolite.